Over tea in his opulent apartment on the Beirut seafront, the shutters down even in daylight, Marwan Hamadeh showed visitors photographs of his bleeding, disfigured face after he survived an assassination attempt in late 2004. The bomb that destroyed his car and decapitated his driver left him with terrible injuries and a burning conviction that Lebanon must change.

Hamadeh, now a minister in the western-backed government, was the first target of a murderous campaign against Syria's Lebanese enemies. Its best known victim was the former prime minister, Rafiq al-Hariri, who died with 22 others three years ago in a huge explosion that tore apart his convoy in the heart of the capital.

Beirut's notorious Valentine's Day massacre will be marked tomorrow by a rally in Martyrs Square. The commemoration is a show of strength by the Christian-Sunni-Druze coalition that has been in power since the "intifada" that forced the Syrians out, though this fragile country remains under siege - and deeply fearful for the future.

"I have not a single doubt that the Syrians killed Rafiq," Hamadeh insisted. "They had the government, the intelligence, their own army and they thought it would go unpunished."

Nowadays he only goes out under guard - and never, ever, takes his children or grandchildren in his car.

Beirut is a city of honking cars, beautiful people in smoke-filled cafes and walkers enjoying the sun on the famous Corniche overlooking the Mediterranean. But party flags and posters are sprouting on neighbourhood boundaries, with rumours of militias rearming and nervous comparisons with the bad old days. Emigration is up and evidence of depression is rife.

"I'm certainly not going to any demonstrations," said Hassan al-Nousouly, a Sunni driver negotiating the dense traffic on Hamra street. "It could be risky. I'll be staying at home with my kids."

On Sunday night there was gunfire between factions after an incendiary speech by Walid Jumblatt, the veteran Druze leader, who taunted Hizbullah - the dominant force in the Syrian-backed opposition. "You want war?" he asked. "Ahlan wa sahlan - you are welcome."

The worst recent incident came last month when seven Shias protesting about power cuts were shot dead by the army - especially alarming since that is the one neutral institution in the country. Suspicions abound of a deliberate provocation, just like the one in 1975 when Christian fighters machine-gunned a bus of Palestinians after the killing of a Christian.

On January 27, though, Hizbullah reacted with the discipline that has made it the most formidable fighting force in Lebanon and helped it claim victory in the 2006 war. "We were given strict orders not to fire back," said a fighter in the Beirut suburb of Haret Hreik, where gaping holes and rubble mark Israel's air strikes. "If we had, then all hell would have broken out."

Days earlier, another bomb killed a police officer investigating the Hariri case and other deaths. "These are all messages," said a government official. "But this is Lebanon: you have to decide where you think the messages are coming from."

Plans to convene parliament to elect a new president have been postponed 14 times since November, with Arab League mediation unable to bridge the gaps and many wondering whether the politicians really want a deal.

The prime minister's office has been blockaded for more than a year by supporters of Hizbullah and General Michel Aoun, its Christian ally. It is as if Whitehall was permanently sealed off on three sides by demonstrators, with one access route for the government protected by armoured cars, soldiers, and razor wire.

Disputes over the presidency, electoral laws and ministerial appointments are real enough, but they mask Lebanon's most deep-seated existential issues - the persistence of confessional politics and a Christian community that has long been overrepresented at the expense of Muslims.

"Hizbullah and their allies will eventually have a bigger role in government, and they should," said commentator Rami Khouri. But Hizbullah, the government demands, must disarm, ending the existence of a state within the state with the power to decide on war and peace.

Perpetuating Lebanon's problems, as ever, are the machinations and interests of outsiders as distant as Washington and Tehran. Syria retains the power to intimidate despite the removal of its troops. Hizbullah, rearmed with missiles for another round with Israel, is a strategic ally for Iran. Saudi Arabia's rifts with Syria are just one reason for its generous funding for the Beirut government.

So far the war is largely one of words. But there are worries about young people whose politics are tribal but who do not remember the cost of 15 years of civil war. The fear is that Lebanon's next conflict will pit Shias against Sunnis.

"The divide is deep and along sectarian lines and tension is high," said Farid al-Khazen, a Christian opposition MP. "That doesn't mean we are heading for war, but there's no solution either."

Others are not so sure. "It's getting dangerous," argued Timur Goksel, who lectures at Beirut's American University. "Everyone is aware that civil war is an expensive game, even though there isn't the same level of militarisation now and the Palestinians aren't a factor any more. But the dynamics are scary and you can't stop them until they've run their course. Things can easily get out of hand on the streets."